1. Field of the Invention
The present invention relates to an apparatus and method for identifying tissue types using interferometric ranging during needle biopsy. More particularly, the present invention relates to an imaging system including a needle probe and algorithms for detecting various tissue types during a biopsy. Also provided is a method for differentiating tissue types using the imaging system.
2. Background of the Invention
A significant cause of inefficiency of intraoperative and biopsy procedures is the inability of a physician to identify tissue type by gross inspection. For example, head and neck surgeries, the inability to differentiate muscle, fat, lymph node, and parathyroid glands by gross inspection leads to unnecessary operative time, resulting in an increase in the cost of these procedures. Further, when not guided by an imaging modality, fine needle aspiration biopsies yield non-diagnostic tissue in 25% to 35% of cases. In medicine, there is a significant need for an inexpensive, portable, and efficient way for identifying tissue type.
The use of optical coherence tomography and confocal microscopy in needle probes has been previously described. These needle probes allow physicians to acquire images of tissue. However, these conventional needle probes have certain shortcomings. The methods used in these needle probes require imaging a single focused spot on a sample by scanning the spot in two dimensions in order to produce a two dimensional image of the subject. The scanning and imaging requirements of these known imaging needle probe systems require complex and expensive disposable components, as well as console components. Many components of existing imaging needle probes require complex and expensive construction making routine use of the needle probes a practical impossibility. Further, current imaging needle probes use complex and expensive custom syringes, which may not be sterilizable or disposable.
In the past, research has been performed to evaluate the use of low-coherence interferometry (“LCI”) imaging for tissue diagnosis. Optical coherence tomography (“OCT”) is LCI imaging that is performed by obtaining many axial scans while scanning a sample arm beam across a specimen, creating a two dimensional image. In order to perform LCI imaging, several strict requirements must be met by the conventional systems, including use of:                1. high speed reference arm delay scanning (at least 1,000 scans/second),        2. a high power broad bandwidth source (at least 5 mW),        3. a complex probe (must have at least one lens and a scanning mechanism),        4. an expensive data acquisition apparatus, and        5. an image display.These requirements of the conventional systems dramatically increase the cost of OCT systems and OCT probes.        
It would be desirable to have a low cost and accurate imaging system, process and needle biopsy probe having sufficient resolution that can be used by physicians with little additional training. It would also be desirable to have a needle biopsy probe that would use conventional syringe and needle combinations to avoid the high cost of developing and manufacturing custom barrels or needles. Such an exemplary system would also desirably be able to provide real time, or near real time, feedback regarding progress and location of the biopsy needle. Such a probe should also be able to identify various tissue types and interfaces and be able to alert a user when a target site has been reached or if an inappropriate tissue has been encountered. Interfaces are refractive index interfaces which occur when one tissue having optical refractive index is adjacent to another. The refractive index is unique to the molecular constituents of tissue and therefore interfaces occur throughout tissue. These refractive index interfaces may give rise to scattering which is the signal detected by LCI and OCT.
Other features and advantages of the present invention will become apparent upon reading the following detailed description of embodiments of the invention, when taken in conjunction with the appended claims.